Search Results (14)

Relying on an engineering case, this study establishes an analysis model using PLAXIS 3D and GeoStudio, and compares and analyzes the slope deformation and internal force of the supporting structure with different slope grades and different platform widths at the same height. The results show that the greatest displacement manifests in the lower segments of the slope, which is 12.99 mm, and the maximum anchoring force manifests in the mid-level and lower segments of the slope, which is 288.1 kN. A close correlation is observed between the simulated horizontal displacement of the slope, the maximum axial force of the anchor cable, and the corresponding field measurement results, indicating that the model parameters are satisfactory and that the resulting calculations are reliable. In consideration of the comprehensive stability of the slope, the stability coefficient increased by approximately 1.42% with two-stage slope support and by about 3.48% with four-stage slope support. The axial force of anchor cables was reduced by around 9.5% under two-stage grading, while four-stage grading decreased the maximum axial force of the middle–lower anchors by nearly 27%. The distance between the entrance and exit of the overall sliding surface and the slope surface also decreases with the increase in slope grading and platform width. This study systematically evaluates the combined effects of slope grading, platform width, and frame prestressed anchors. When site conditions permit, slope grading should be prioritized over simply widening the platform, as grading more effectively enhances slope stability and reduces anchor cable loads. Full article

Rainfall can easily cause local sliding and collapse of carbonaceous mudstone deep road cut slopes. In order to study the strength characteristics of carbonaceous mudstone under different water environments, large-scale horizontal push shear tests were conducted on carbonaceous mudstone rock masses in their natural state and after immersion in saturated water. The push shear force–displacement relationship curve and fracture surface shape characteristics of carbonaceous mudstone samples were analyzed, and the shear strength index of carbonaceous mudstone was obtained, and numerical simulations on the stability and support effect of carbonaceous mudstone slopes were conducted. The research results indicate that carbonaceous mudstone can exhibit good structural properties and typical strain softening characteristics under natural conditions. The fracture surface, shear strength, and shear deformation process of carbonaceous mudstone samples will undergo significant changes after being soaked in saturated water. The average cohesion decreases by 33% compared to the natural state, and the internal friction angle decreases by 15%. The numerical simulation results also fully verify the attenuation of mechanical properties of carbonaceous mudstone after immersion, as well as the effectiveness of prestressed anchor cables and frame beams in supporting carbonaceous mudstone slopes. The research results provide an effective method for understanding the shear performance of carbonaceous mudstone and practical guidance for evaluating the stability and reinforcement design of carbonaceous mudstone slopes. Full article

Traditional monolithic precast and precast prestressed concrete joints often face challenges such as complex steel reinforcement details and low construction efficiency. Grouting sleeve connections may also suffer from quality issues. To address these problems, a new precast prestressed concrete frame beam-column exterior joint using ultra-high-performance concrete (UHPC) for connection (PPCFEJ-UHPC) is proposed. This innovative joint lessens the amount of stirrups in the core area, decreases the anchorage length of beam longitudinal reinforcement, and enables efficient lap splicing of column longitudinal reinforcement, thereby enhancing construction convenience. Cyclic loading tests were conducted on three new exterior joint specimens (PE1, PE2, PE3) and one cast-in-place joint specimen (RE1) to evaluate their seismic performance. The study concentrated on failure modes, energy dissipation capacity, displacement ductility, strength and stiffness degradation, shear stress, and deformation’s influence on the longitudinal reinforcement anchoring length and axial compression ratio. The results indicate that the new joint exhibits beam flexural failure with minimal damage to the core area, unlike the cast-in-place joint, which suffers severe core area damage. The novel joint exhibits at least 21.7% and 6.1% improvement in cumulative energy consumption and ductility coefficient, respectively, while matching the cast-in-place joint’s bearing capacity. These characteristics are further improved by 5.5% and 10.7% when the axial compression ratio is increased. The new joints’ seismic performance indices all satisfy the ACI 374.1-05 requirements. Additionally, UHPC significantly improves the anchoring performance of steel bars in the core area, allowing the anchorage length of beam longitudinal bars to be reduced from 16 times of the diameter of reinforcement to 12 times. Full article

This paper focuses on the analysis of the stress state of a large-span frame pier-continuous box girder bridge with pier crossbeams anchored by pier crossbeams on the main pier of the Guangfo-Zhao Expressway. The bridge is constructed by the cantilever method, and a refined finite element model of the entire bridge is established using the finite element software Midas/FEA to analyze the stress state of the frame pier during the cantilever construction process. It is found that under the possible combined action of an unbalanced load during construction, the torsional resistance of the frame pier crossbeam does not meet the requirements of the design code. In order to eliminate the torsion of the frame piers, counterweights were used to monitor the frame piers during the construction of the box girders. In this paper, the theoretical calculation formula of the inclination angle of the end section of the frame pier crossbeam with the change of unbalanced bending moment, the calculation formula of the relationship between the horizontal displacement of the frame pier and the unbalanced bending moment, and the calculation formula corresponding to the relationship with the water tank counterweight are derived using the structural mechanics method. Two monitoring methods for the frame pier are proposed. In the construction monitoring of the bridge, the numerical fitting formula obtained by finite element numerical analysis calculation is compared with the calculated formula obtained by substituting the design parameters of the frame pier into the theoretical formula. The basic constants in both formulas are basically equal, verifying the correctness of the monitoring calculation formula proposed in this paper for the torsional resistance of the frame pier crossbeam. The applicability of the two monitoring methods is also compared and analyzed. This paper takes the main pier of Chaoyang overpass’s mainline bridge as the engineering background, which adopts the framework pier with a large-span prestressed concrete continuous box girder bridge. It analyzes the torsional state of the beam of the framework pier during the bridge construction process and conducts research on the construction monitoring of the framework pier crossbeam, providing valuable references for the construction monitoring of framework pier crossbeams in the construction of large-span framework pier continuous bridges in the future. The research results of this paper can provide assistance for the construction monitoring of similar projects. This paper’s innovation primarily resides in employing structural mechanics methods to compute the torsion of frame piers. On this basis, a simplified beam torsion calculation formula is proposed to strengthen its practical application in construction monitoring. The findings of this paper can help in the construction monitoring of similar projects. Full article

Due to the intricate and volatile nature of the service environment surrounding prestressing anchoring materials, stress corrosion poses a significant challenge to the sustained stability of underground reinforcement systems. Consequently, it is imperative to identify effective countermeasures against stress corrosion failure in cable bolts within deep underground environments, thereby ensuring the safety of deep resource extraction processes. In this study, the influence of various coatings on the stress corrosion resistance of cable bolts was meticulously examined and evaluated using specifically designed stress-corrosion-testing systems. The specimens were subjected to loading using four-point bending frames and exposed to simulated underground corrosive environments. A detailed analysis and comparison of the failure patterns and mechanisms of specimens coated with different materials were conducted through the meticulous observation of fractographic features. The results revealed stark differences in the stress corrosion behavior of coated and uncoated bolts. Notably, epoxy coatings and chlorinated rubber coatings exhibited superior anti-corrosion capabilities. Conversely, galvanized layers demonstrated the weakest effect due to their sacrificial anti-corrosion mechanism. Furthermore, the effectiveness of the coatings was found to be closely linked to the curing agent and additives used. The findings provide valuable insights for the design and selection of coatings that can enhance the durability and reliability of cable bolts in deep underground environments. Full article

To address issues with excessive displacement, deformation, and insufficient load bearing capacity in high-fill-reinforced soil-retaining walls, a novel reinforced soil–frame anchor combination system was developed. Despite the limited existing research on its mechanical properties and synergy, a physical model test was conducted to investigate the system’s behavior. The test focused on the horizontal displacement of the frame beam wall, grid strain, wall back earth pressure, and anchor strain. Results indicated that anchor prestress effectively controlled horizontal deformation, limiting it to 65% of the original displacement value. Additionally, as the top load increased, strain in the bottom bars showed minor changes, while strain in the middle and upper bars exhibited significant sensitivity to load variations. The application of anchor prestress reduced strain in each reinforcement layer, enhancing the geogrid’s load bearing capacity. Furthermore, anchor prestress altered the distribution of earth pressure within the system, establishing a synergistic relationship between reinforced soil and frame beam anchors. This stress transfer mechanism improved overall system performance, as demonstrated in the test. Overall, the study confirmed the benefits and superior performance of the combined system. Full article

Frame beams with anchor cables constitute a crucial method for slope reinforcement projects. With the development of fabricated structures, there has been an increasing focus on precast prestressed frame beams with anchor cables. This paper presents a field test conducted in Yunnan, China and numerical simulations to analyze the structure behavior of three types of frame beams with a 600 kN anchoring force: cast-in-situ frame beams, precast prestressed frame beams, and precast prestressed frame beams with connections. The results showed that: (1) Although all three types of frame beams met the design requirements for a 600 kN anchoring force capacity, the volume of precast prestressed frame beams constituted only 57% of that of the cast-in-situ frame beams. (2) The maximum bending moment for the precast prestressed frame beams with connections was 60 kN·m less than that for the cast-in-situ frame beams. (3) The field test results for bending moments exceeded the values obtained from the numerical simulation. When using a numerical simulation to study the bending moments of the anchor frame beams, it is acceptable to apply appropriate amplifications to the numerical results. (4) Among the three types of frame beams with cables, the precast prestressed frame beams with connections exhibited the best structural performance. Full article

Because of the current situation where the stability research of filled-slope reinforced by a frame with prestressed anchor-plates lags behind the actual engineering application, based on the ultimate balance theory, the calculation formulas of stability factor under the four arc slip surface of filled-slopes reinforced by a frame with prestressed anchor-plates are derived by using the improved Bishop method; the corresponding search method of the most dangerous slip surface is given and the calculation formulas of the pullout force of anchor-plates are improved. Based on two examples, the stability results calculated by the proposed algorithm are compared with those calculated by PLAXIS 3D and GeoStudio 2012 finite element software, and the following conclusions are drawn. (1) The improved pullout force of anchor-plates takes into account the friction of the front and rear surface of the anchor-plate and the effect of cohesion of fill soil in the passive earth pressure on the front end of the anchor-plate, which makes the force of the anchor-plate more complete. (2) The stability factor of example 1 calculated by this method differs from the results simulated by PLAXIS 3D and GeoStudio 2012 by 4.6% and 7.1%, respectively; the stability factor of example 2 calculated by this method differs from the results simulated by PLAXIS3D and GeoStudio 2012 by 3.2% and 4.5%, respectively, which can meet the engineering requirements. (3) The stability analysis method of filled-slope reinforced by a frame with prestressed anchor-plates that is proposed is reasonable and suitable for any arc slip surface in the filled-slope reinforced by a frame with prestressed anchor-plates, and it provides some guiding values for the design of practical engineering. Full article

The traditional connections and reinforcement details of precast RC frames are complex and cause difficulty in construction. Ultra-high-performance concrete (UHPC) exhibits outstanding compressive strength and bond strength with rebars and strands; thus, the usage of UHPC in the joint core area will reduce the amount of transverse reinforcement and shorten the anchoring length of beam rebars as well as strands significantly. Moreover, the lap splice connections of precast columns can be placed in the UHPC joint zone and the construction process will be simplified. This paper presented a novel joint consisting of a precast pretensioned prestressed concrete beam, an ordinary precast reinforced concrete (RC) column, and a UHPC joint zone. To study the seismic performance of the proposed joints, six novel interior joints and one monolithic RC joint were tested under low-cyclic loads. Variables such as the axial force, the compressive strength of UHPC, the stirrup ratio were considered in the tests. The test results indicate that the proposed joints exhibit comparable seismic performance of the monolithic RC joint. An anchorage length of 40 times the strands-diameter and a lap splice length of 16 times the rebar-diameter are adequate for prestressed strands and precast column rebars, respectively. A minimum column depth is suggested as 13 times the diameter of the beam-top continuous rebars passing through the joint. In addition, a nine-time rebar diameter is sufficient for the anchorage of beam bottom rebars. The shear strength of UHPC in the joint core area is suggested as 0.8 times the square root of the UHPC compressive strength. Full article

Considering the interaction among anchor cable, frame beam and rock mass, a new model of prestress loss of anchor cable was established. The accuracy and applicability of the new model were verified by comparing the field monitoring data and the calculation results of existing models. In addition, based on the new model, the effect of the re-tension of the anchor cable at different time nodes was analyzed, and the later compensation time of anchor cable prestress was discussed. The research shows that: the accuracy of the new model is higher after considering the effect of the frame beam, the new model can not only calculate the loss of prestress of anchor cable, but also accurately predict the time when the prestress of anchor cable reaches the stable stage. The ideal effect of prestress compensation can be achieved when the anchor cable is re-tensioned at each time point after 20 days of the construction completed. The original prestress loss of the anchor cable is different, and the re-tension effect is also different, the greater the loss of the original prestress of the anchor cable, the more obvious the prestress compensation effect during the re-tension. Full article

In order to investigate the seismic performance of prestressed concrete rocking frame (PCRF), a theoretical model based on rigid body is established for a one-story single-span PCRF. The PCRF studied in this paper has the connecting interfaces set at the column feet and at the inner faces of the beam–column joints, allowing the columns to be uplifted with the accompanying separation of the beam–column interface and rotation of the beam and column around the interface. The tendons are arranged along the centerline of the beam and columns. The connections between the beam and columns and the anchoring of columns are accomplished by prestressing the tendons. The theoretical model consists of a rigid beam, rigid columns and elastic tendons. The governing motion equation of the PCRF is derived based on the model and a numerical solution of the equation of motion is obtained. The energy dissipation of the PCRF is analyzed and the calculation method for the coefficient of restitution is derived. Time history analysis and parameter analysis of seismic response of the PCRF are conducted and the results show that the PCRF has promising seismic behavior. Full article

The concrete stress behavior and cause of cracking at the anchorage zones of top and bottom slabs of a post-tensioned prestressed concrete box beam were studied. Based on the complex stress distribution under local anchor problem for the Yichang Yangtze River Bridge, which is the longest continuous rigid frame arch railway bridge in the world, model tests were conducted. Two full-scale specimens of top and bottom slabs were fabricated and gradually loaded based on principle of equivalent stress. The goal was to analyze the longitudinal and transverse stress distributions of cross sections of specimens at various loading cases during the experiment. From the experimental results, it can be concluded that the mechanical behavior of the concrete and steel bars were in good agreement when prestressed tendons were loaded. Tensile stress of concrete in prestressed anchorage zone gradually increased and surpassed the ultimate tensile strength of concrete with the increasing load. Consequently, local longitudinal cracking was formed at the anchorage block. Some recommendations to avoid the concrete at the anchorage zone continuing to crack are summarized in this paper. Full article

The bridges will be in service in a complex environment for over 100 years under the increasing traffic loading. So the long-term performance determines their safety and durability. Limited by the test condition and ability, present researches are mostly focused on the natural environment exposure tests and artificial environment acceleration tests for materials and components. According to the service conditions and load characteristics of the bridges, the accelerated test system was developed for bridge structure under combined environment and loading. This test system consists of three parts, including a large environment box, loading system and monitoring system. The environment box is 32 m long, 4 m wide and 3/10 m high. It is divided into 5 working bins which can be used alone or in combination. The simulation environment includes high temperature drying, low temperature freezing and thawing, damp cold, high temperature cycle, salt fog, rain, carbonation, temperature and humidity alternating and optical spectrum light aging environment. The servo static and dynamic loading system adopts Servotest actuators with loading tonnage from 400 tons to 50 tons. And the total tonnage is 1200 tons. Aided by the prestressed concrete reaction wall, steel structure frames and the anchor system, the external loading system can exert dynamic and static loads on the bridge structure in the environment box. And the non-contact nondestructive monitoring system can real-time monitor and measure their long-term deformation, internal force, cracking and other damage. This artificial acceleration test system can support the Chinese Long Term Bridge Program, and improve the safety, durability, reliability and long service life of bridges and other civil engineering. Full article

The potential for monitoring the construction of post-tensioned concrete beams and detecting damage to the beams under loading conditions was investigated through an experimental program. First, embedded sensors were investigated that could measure pre-stress from the fabrication process to a failure condition. Four types of sensors were installed on a steel frame, and the applicability and the accuracy of these sensors were tested while pre-stress was applied to a tendon in the steel frame. As a result, a tri-sensor loading plate and a Fiber Bragg Grating (FBG) sensor were selected as possible candidates. With those sensors, two pre-stressed concrete flexural beams were fabricated and tested. The pre-stress of the tendons was monitored during the construction and loading processes. Through the test, it was proven that the variation in thepre-stress had been successfully monitored throughout the construction process. The losses of pre-stress that occurred during a jacking and storage process, even those which occurred inside the concrete, were measured successfully. The results of the loading test showed that tendon stress and strain within the pure span significantly increased, while the stress in areas near the anchors was almost constant. These results prove that FBG sensors installed in a middle section can be used to monitor the strain within, and the damage to pre-stressed concrete beams. Full article